Method of adapting the data rate during transmission of variable bit-rate data streams

Abstract

A method of adaptively controlling the data rate in a transmission channel carrying a packet data signal corresponding to a data stream of variable data rate is suggested. In accordance with the method the variability of the transmission channel, the data rate requirement of the data stream, and the capacity of the transmission channel are determined. Then, the data rate is adapted so that the transmission channel capacity exceeds the data rate requirement of the data stream, and the next time instant for data rate probing and adaptation is determined based upon the transmission channel variability and data stream rate requirement.

1 . A method of adaptively controlling a data rate in a transmission channel carrying a variable bit rate video signal, including:
 determining a variability of the transmission channel in_a current window;   determining a data rate requirement of the video signal during a next window;   determining a capacity of the transmission channel during the next window;   adapting the data rate for the next window so that the capacity exceeds the data rate requirement; and   determining a time instant of the next data rate adaptation based upon transmission channel variability and video data rate requirement, wherein the window size is variable, and wherein the window size is chosen in accordance with the variability of capacity of the transmission channel in a current window and/or the data rate requirement of the video signal in the next window.   
     
     
         2 . The method of  claim 1 , wherein determining the variability of the transmission channel includes measuring one or more signal strength values and/or error rate values, the error rate values including one or more of frame error rate, packet error rate, bit error rate values over a time window, and computing their variability. 
     
     
         3 . The method of  claim 1 , wherein determining the data rate requirement of the video signal includes buffering at least a part of a video signal to be transmitted and analyzing the data rate of the buffered video signal. 
     
     
         4 . The method of  claim 1 , wherein determining the capacity of the transmission channel includes measuring one or more signal strength and/or error rate values, the error rate values including one or more of frame error rate, packet error rate, bit error rate of the video signal, and relating the measured value to a transmission channel throughput, or directly measuring transmission channel throughput, over a time window. 
     
     
         5 . The method of  claim 1 , wherein adapting the data rate includes maintaining a current data rate if the estimated transmission channel capacity exceeds the data rate requirement of the video signal until the next data rate adaptation is scheduled, or selecting a different eligible data rate which provides a transmission channel capacity that exceeds the data rate requirement of the video signal. 
     
     
         6 . The method of  claim 5 , wherein the selection of a different eligible data rate includes probing the transmission channel at different data rates by repeatedly selecting and transmitting at different data rates and determining the respective capacity of the transmission channel, and selecting a data rate whose capacity is higher than the data rate requirement of the video signal. 
     
     
         7 . The method of  claim 5 , wherein probing the transmission channel includes a first step of determining probing direction by probing at the next eligible data rate higher than the current data rate and at an the next eligible data rate lower than the current data rate; and a second step of continuing probing at higher data rates if the capacity of the next eligible higher data rate is higher than the capacity of the next eligible lower data rate, or continuing probing at lower data rates if the capacity of the next eligible lower data rate is higher than the capacity of the next eligible higher data rate, until a data rate with higher capacity than the data rate requirement of the video signal is found or until all eligible data rates are probed. 
     
     
         8 . The method of  claim 1 , wherein determining a time instant of the next data rate adaptation includes determining a time window during which a data rate of the video signal remains below a predetermined threshold and/or comparing the data rate variability of the transmission channel to a low and high threshold, wherein a time window length is decreased if the variability exceeds the high threshold, wherein the time window length is increased if the variability falls below the low threshold, and wherein the time window length is maintained if the variability remains between the two thresholds. 
     
     
         9 . The method of  claim 8 , wherein the time instant of the next data rate adaptation is located at the boundary of a time window. 
     
     
         10 . The method of  claim 8 , wherein adapting the data rate is performed at a time within a time window when the data rate of the video signal is below a predetermined threshold.